In eukaryotes transcription initiation requires the action of several proteins acting in concert to initiate mRNA production. Two cis-acting regions of DNA have been identified that bind transcription initiation proteins. The first binding site located approximately 25-30 bp upstream of the transcription initiation site is termed the TATA box. The second region of DNA required for transcription initiation is the upstream activation site (UAS) or enhancer region. This region of DNA is somewhat distal from the TATA box. During transcription initiation RNA polymerase II is directed to the TATA box by general transcription factors. Transcription activators which have both a DNA binding domain and an activation domain bind to the UAS region and stimulate transcription initiation by physically interacting with the general transcription factors and RNA polymerase. Direct physical interactions have been demonstrated between activators and general transcription factors in vitro, such as between the acidic activation domain of herpes simplex virus VP16 and TATA-binding protein (TBP), TFIIB, or TFIIH (Triezenberg et al. (1988) Gene Dev. 2:718-729; Stringer et al. (1990) Nature 345:783-786; Lin et al. (1991) Nature 353:569-571; Xiao et al. (1994) Mol. Cell. Biol. 14:7013-7024).
A third factor that is involved in the interaction is the adaptor proteins. It is thought that adaptor proteins serve to mediate the interaction between transcriptional activators and general transcription factors. Functional and physical interactions have also been demonstrated between the activators and various transcription adaptors or coactivators. These transcription coactivators normally cannot bind to DNA directly, however they can "bridge" the interaction between transcription activators and general transcription factors (Pugh and Tjian (1990) Cell 61:1187-1197; Kelleher et al. (1990) Cell 61:1209-1215; Berger et al. (1990) Cell 61:1199-1208).
In humans Epstein-Barr virus nuclear antigen 2 (EBNA 2) activates transcription of specific genes essential for B-lymphocyte transformation. EBNA 2 has an acidic activation domain which interacts with general transcription factors TFIIB, TFIIH, and TAF40. It has been shown that EBNA 2 is specifically bound to a novel nuclear protein, p100, and that p100 can coactivate gene expression mediated by the EBNA 2 acidic domain. Interestingly, p100 also appears to be essential for normal cell growth, since it has been shown that cell viability is reduced by antisense p100 RNA and restored by sense p100 RNA expression (Tong et al., (1995) Mol. Cell Biol.15(9):4735-4744).
Accordingly, the availability of nucleic acid sequences encoding all or a portion of ALY transcription coactivator proteins would facilitate studies to better understand transcription in plants and ultimately provide methods to engineer mechanisms to control transcription.